import sys
import math


class Solution:
    def count_0(self, N, M=10):
        zero_count = 0
        for i in range(5, N+1, 5):
            temp = i
            while temp % 5 == 0:
                zero_count += 1
                temp //= 5
        return zero_count


if __name__ == '__main__':
    line = sys.stdin.readline().strip()
    N, M = list(map(int, line.split()))
    x = Solution()
    print(x.count_0(10, 5))